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SURF
21-Oct-2012, 04:07
Hi! Not everybody owns USAF 1951 resolution target for scanner tests and even if owns it is rather hard to see how linear is the focus over the whole scanning area with its help.

New solution - resolution target made from the LCD TFT dead monitor panel. Inside there is a lot. :) See 8000 dpi 100% crop. And the same picture is anywhere there. Beware! It is of the thin glass and you need to disassemble it. I did not manage to make it without braking the glass but it depends on the TFT panel I think. Using water while disassembly helps.

Regards
Al

ramon
24-Oct-2012, 08:13
Good tip !

Also I have found resolution targets on the last image of some microfiche.

Don't know if all microfiches must have the resolution target or not.

Lightbender
15-Nov-2012, 00:11
I prefer to use a crisp new 1$ dollar bill.

C. D. Keth
15-Nov-2012, 00:32
You guys do know that a real resolution target, printed so that you can read it objectively with real LPMM numbers, are not that expensive, right? Here you go (http://www.filmtools.com/ceproprech4.html), $22.50 to do it properly and objectively.

Leigh
15-Nov-2012, 08:31
No linear target will test a scanner properly unless it's absolutely square with the sensor array and the axis of movement.

Also, you get sampling errors that can totally obscure the real resolution of the scanner. Permit me an example.

Say you have a sensor pitch of 1000 pixels per inch, and a target pattern of 500 line pairs per inch (500 white, 500 black).
In a perfect world, if the target is exactly aligned with the sensors, you'll get a clean 500lpi pattern.
However, if the target is offset by 1/2000th of an inch, you'll get a solid gray image with no discernible pattern.
This is because each individual sensor sees 1/2 white and 1/2 black.

The USAF 1951 target and the one that Christopher suggested both suffer from this problem.
These targets were designed for film, which does not suffer from the sampling problem that's inherent in a scanner.

The best target for scanners is the starburst, with radial lines converging on a point.

The dollar bill that was suggested earlier is also good because it has lines in all directions combined with arcs.
Please note that a $1 bill works just as well for this purpose as a $100, and is much cheaper. :D

- Leigh

Jim Jones
15-Nov-2012, 10:19
This resolution chart for comparative tests may be freely replicated or published
http://www.largeformatphotography.info/forum/attachment.php?attachmentid=83605&d=1324394640.

Nathan Potter
15-Nov-2012, 10:20
Using a TFT panel as a resolution target can only yield qualitative results. To obtain quantitative data on resolution several things should be considered.

The feature sizes on the panel must be calibrated.
Feature sizes appear to be of very limited range.
The panel needs to be at the plane of best focus.
The Dmax and Dmin of the image on the panel will influence the MTF derived from the scans.
The resolution results depend on the method of measurement of the scanned image. (you can use PS for that).
The scanner is a digital device and is subject to the problems pointed out by Leigh above - orientation.

Despite all of that, I think you are after only a vague notion of scanner capability so go for it.

If you want to learn more about the complexity of resolution testing check out the following;

http://www.gpsinformation.org/jack/photo-test/pics/lens-tests.html
http://www.the-digital-picture.com/Help/ISO-12233.aspx (shows a standard ISI 12233 test chart)
http://www.aig-imaging.com/imatest.html (state of the art software and targets for resolution determination)

Nate Potter, Austin TX.

C. D. Keth
15-Nov-2012, 10:38
Leigh, perhaps a chart like this (http://www.filmtools.com/pushinty7a9.html) would be better? It's more expensive but it's the same principle but using concentric circles rather than straight lines.

Another thing we'll do with the straight line century charts when prepping for a movie is we'll shoot them a couple times at random angles, anything except plumb and level to the sensor.

Leigh
15-Nov-2012, 12:58
Leigh, perhaps a chart like this (http://www.filmtools.com/pushinty7a9.html) would be better
Yes, definitely. I've not seen that particular target before.
I think it will take care of the orientation and sampling errors quite nicely.

However, it's 10" x 10" and rigid (mounted on fibre board).
My V750 (and most others) have the glass recessed below the metal housing.

- Leigh

SURF
16-Nov-2012, 07:28
Well. Thank you all for the replies. Must say that they gave me the feeling that main idea was completely lost in most replies. I will repeat from original post to make it more clear:

... it is rather hard to see how linear is the focus over the whole scanning area with its help.


There is not a lot of things in this world that have such a fine repeating structure as the TFT matrix glass.

Good luck
Al

C. D. Keth
16-Nov-2012, 23:57
Yes, definitely. I've not seen that particular target before.
I think it will take care of the orientation and sampling errors quite nicely.

However, it's 10" x 10" and rigid (mounted on fibre board).
My V750 (and most others) have the glass recessed below the metal housing.

- Leigh

That target really doesn't go fine enough to be scanned directly anyway. Their intent, and mine in suggesting it, is that it be photographed in the prescribed way (I think it's at a distance of 60x the focal length) and the negative scanned, testing the system as a whole.

Leigh
17-Nov-2012, 00:01
Oh. OK.

- Leigh

ramon
18-Nov-2012, 08:53
Hi,

I want to clarify that I have found NBS 1010a resolution targets in the last image of some microfiche.

This resolution targets are specific for microfilm / microfiche and scanning, and you can obtain lpmm directly.

Price for NBS1010a at edmundoptics starts from $165 USD, at aig-imaging starts from $99 USD.

I get mine (the microfiche) from some (in)famous auction site at $3:


http://www.largeformatphotography.info/forum/showthread.php?77506-USAF-1951-test-chart-in-SVG-format&p=746932&viewfull=1#post746932

SURF
19-Nov-2012, 05:43
Hi Ramon,

that's interesting. Someone has to scan those at high real resolution.

Good luck
Al

Hi,

I want to clarify that I have found NBS 1010a resolution targets in the last image of some microfiche.


http://www.largeformatphotography.info/forum/showthread.php?77506-USAF-1951-test-chart-in-SVG-format&p=746932&viewfull=1#post746932